1. Field of the Invention
The present invention relates to the synthesis of Li2Mn4O8+z, with z greater than zero and less than one, prepared from LiMnO4 and an appropriate complimentary compound, such as MnOOH, MnO2 or MnCO3 precursors, and its use in highly oxidized lithium manganospinels.
2. Brief Description of the Related Art
Lithium manganospinels have been investigated as lithium insertion cathodes for lithium-ion batteries (see e.g., A. de Kock, M. H. Rossouw, L. A. de Picciotto, M. M. Thackeray, W. I. F. David and I. M. Ibberson. Mater. Res. Bull. 25 (1990); M. M. Thackeray, A. de Kock, M. H. Rossouw, D. Liles, R. Bittihn and D. Hoge. J. Electrochem. Soc. 139 (1992); M. M. Thackeray and M. H. Rossouw. J. Solid State Chem.113 (1994); M. M. Thackeray, A. de Kock and W. I. David. Mat. Res. Bull. 28 (1993); M. M. Thackeray and M. H. Rossouw. J. Solid State Chem. 113 (1994); and R. J. Gummow, A. de Kock and M. M. Thackeray. Solid State Ionics 69 (1994)). The difficulty in preparing the fully oxidized material Li2Mn4O9, in a reproducible manner, is well known (see e.g., C. Masquelier, M. Tabuchi, K. Ado, R. Kanno, Y. Kobayashi, Y. Maki, O. Nakamura and J. B. Goodenough. J. Solid State Chem. 123 (1996)). Strict control of experimental conditions such as temperature, time, particle size of the precursor materials, and oxygen partial pressure has been essential for producing fully oxidized, single-phase material. Studies to date, however, show clearly that the fully oxidized Li2Mn4O9 phase has never been prepared successfully.
Many compounds and synthesis methods have been tried in attempting to produce suitable cathode active materials for rechargeable lithium batteries. Compounds, which function as lithium insertion electrodes, include LiCoO2 and LiTiS2. However, lower cost and higher energy density materials are desirable. In particular, lithium-manganese-oxides contain multiple attractive properties of high cell voltage, long shelf life, wide operating temperature and relatively non-toxicity (see e.g., M. M. Thackeray et al., J. Electrochem. Soc. Vol. 139, No. 2, February 1992). Ordinary manganese dioxide, MnO2, cathodes, used in primary lithium/manganese dioxide 3 volt cell, show limited rechargeability in lithium cells. A significant improvement in capacity stability with cycling is obtained with cathodes prepared by reacting gamma MnO2 with lithium hydroxide at moderate temperature (see e.g., N. Furukawa et al. in xe2x80x9cPrimary and Secondary Ambient Temperature Lithium Batteriesxe2x80x9d, J. Gavitno, Z. Takeharn and P Bro, Editors, PV 8-6, p. 557, The Electrochemical Soc. Softbound Proc. Series, Pennington, N.J. (1988)). This reaction results primarily in the formation of a lithium-manganese oxide spinel component with a cubic close-packed oxygen array, which has been shown to be advantageous over one having a hexagonal close-packing arrangement (see e.g., M. M. Thackeray in xe2x80x9cProceeding of MRS Symposium,xe2x80x9d boston, November/December 1988, Vol. 135, p. 585 (1989)).
The present invention includes a process for making Li2Mn4O8+z, wherein z is greater than zero and less than 1, comprising the steps of mixing lithium permanganate with a precursor selected from the group consisting of MnOOH, MnO2 and MnCO3, and heating the mixture effective to form Li2Mn4O8+z, wherein z is greater than zero and less than 1.
The present invention also includes Li2Mn4O8+z, wherein z is greater than zero and less than 1, produced by the process of the present invention.
Furthermore, the present invention includes Li2Mn4O8+z, wherein z is greater than 0.65, and Li2Mn4O8+z, wherein z is less than 0.88.
Additionally, the present invention includes a cathode comprising the Li2Mn4O8+z made by the present process.